The second harmonic generations (SHG) of liquid crystalline main-chain type polymers were investigated. The sample polymers are copolymers of 2-hydroxy-6-naphthoic acid (HNA) with 4-hydroxy-benzoic acid (PHB), in various composition ratios. The SHG of the film samples was greatly affected not only by the polymerization conditions, but also by preparation conditions of the films. SHGs for the samples processed by mechanical stretching and for electrically poled samples were compared. The nonlinear optical coefficients dexpevaluated by Maker Fringe method of the electrically poled samples are 2–3 times larger than that of the mechanically oriented sample whose dexpis about 5pm/V. Trials of Quasi-Phase Matching of periodically inverted-polarized films show very effective to improve SH efficiency. A method mat can control SH efficiency by application of electric field is proposed.